Rename Limited to Clamp

[Ogeon]

I think "Limited" sounds like there will be "limited" and "unlimited" color spaces, but the reality is not as clear cut. It's more that most of them have a typical range. I think it's better to rebrand the trait to an "action" trait, by naming it with a verb, and letting the details be implementation specific. So it will still make sense to have a clamp method even if a color space is only limited by convention, but still could have a theoretically infinite range.

What to do:

• Rename the trait
• Rename is_valid to is_within_bounds or something more appropriate
• Update documentation and examples